Friday, September 9, 2011

The 76 trillion dollar computer game

A paper published today in the Journal of Geophysical Research in essence reveals climate models are not capable of reproducing the observed climate of the past century, much less the future. According to the paper, "few models reproduce the strong observed warming trend from 1918 to 1940," there are "large differences" in the forcings and feedbacks used in various models and that some of these are "unrealistic." In other words, the key inputs and assumptions of the models are not known with reasonable certainty - ergo GIGO. The paper also finds that predicting the range of "future climate change by weighting these models based on their 20th century [performance] is not possible." Translation: climate models are little more than very expensive computer fantasy games that cannot predict the future nor even replicate the past.

In this paper, we breakdown the temperature response of coupled ocean-atmosphere climate models into components due to radiative forcing, climate feedback and heat storage/transport to understand how well climate models reproduce the observed 20th century temperature record. Despite large differences between models' feedback strength, they generally reproduce the temperature response well but for different reasons in each model. We show that the differences in forcing and heat storage/transport give rise to a considerable part of the inter-model variability in global, Arctic and tropical mean temperature responses over the 20th century. Projected future warming trends are much more dependent on a model's feedback strength, suggesting that constraining future climate change by weighting these models based on their 20th century reproductive skill is not possible. We find that tropical 20th century warming is too large and Arctic amplification is unrealistically low in the GFDL CM2.1, MRI CGCM232a and MIROC3.2 hires models due to unrealistic forcing distributions. The Arctic amplification in both NCAR models is unrealistically high due to high feedback contributions in the Arctic compared to the tropics. Few models reproduce the strong observed warming trend from 1918 to 1940. The simulated trend is too low, particularly in the tropics, even allowing for internal variability, suggesting there is too little positive forcing or too much negative forcing in the models at this time. Over the whole of the 20th century, the feedback strength is likely to be underestimated by the multi-model mean.http://www.agu.org/pubs/crossref/2011/2011JD015924.shtml